1. Field of the Invention
The present invention relates to a medical pump adapted for use as a blood pump for a heart-lung machine, blood pump as a substitute for the heart, auxiliary heart, artificial heart, etc.
2. Description of the Related Art
Pumps of various types have already been developed as blood pumps for medical use. These pumps include, for example, roller pumps, finger pumps, positive-displacement blood pumps, rotary blood pumps, centrifugal pumps, and teaspoon-type centrifugal pumps (see "Artificial Organs" Vol. 18, No. 2, pp. 448 to 452). In the roller pumps, blood in an elastic tube is gradually forced out for delivery by stroking the tube by means of a roller. In the finger pumps, blood in an elastic tube is forced out by gradually constricting the tube by means of a compressor. In the positive-displacement pumps, blood is sucked in or pulsed out by reciprocating a piston or diaphragm by means of a check valve at the inlet or outlet. In the rotary pumps, blood is discharged by rotating a rotor to change the capacity of a space between the rotor and a pump housing. In the centrifugal pumps, an impeller is rotated at high speed to apply a centrifugal force to blood, thereby discharging the blood. In the teaspoon pumps, a blade is brought into precession.
According to the roller pumps or finger pumps in which blood is discharged by stroking or constricting the elastic tube, however, blood cells of the blood are liable to be destroyed (or hemolyzed), so that the pumps can hardly stand prolonged use. Since the deformation of the elastic tube requires a lot of energy, moreover, the efficiency of energy conversion is low.
In the positive-displacement pumps, the artificial valve located at the inlet or outlet is very expensive, and blood is liable to coagulate around the valve. Since one pulse requires a capacity equivalent to that of the heart, moreover, the artificial heart, including a drive mechanism therefor, has so large a total capacity that it cannot be easily implanted in the thoracic cavity. Since the internal diaphragm is reciprocated, furthermore, the energy conversion efficiency is lower than in the case of the rotary pumps.
In the rotary pumps, blood is liable to be destroyed by the rotor, and microbism or blood coagulation can be easily caused unless the gap between a rotating shaft and a housing section is fully sealed. Satisfactory sealing between the shaft and the housing section, however, requires engineering skill of a high order.
In the centrifugal pumps, the gap between the rotating shaft and the housing section cannot be fully sealed. In order to solve this problem of sealing, the drive mechanism and the impeller may be magnetically coupled through a housing wall by the use of a permanent magnet. According to this method, however, the pump section must be increased in size, and the energy conversion efficiency is extremely low.
The teaspoon pumps have been developed to cope with these problems. These pumps are based on the principle that a fluid in a vessel can be rotated by bringing a spoon into precession. More specifically, a spoon-shaped blade, having spindle-shaped cut end portions, is caused to make a precessional motion in a casing, thereby fulfilling a turbo-pump function.
In these teaspoon pumps, however, blood at the outer peripheral portion of a pump chamber is stirred by means of the spoon so that the blood is delivered centrifugally. Therefore, the configuration of a passage is so complicated that the manufacture of the pump is difficult and entails higher costs.
Since the single spoon-shaped blade is used in the teaspoon pumps, moreover, the energy conversion efficiency is low.
If the pump chamber is formed into an annular passage through which the blade passes, in order to improve the energy conversion efficiency, the gap between the blade and the wall surface of the annular passage is so narrow that a great shearing force is applied to blood cells of the blood flowing through the gap, thereby causing substantial hemolysis. Since the blood flow near the root of the spoon involves no substantial kinetic energy, moreover, the blood may possibly coagulate at that portion after prolonged use.
In general, blood pumps for medical use are expected to have all of such advantages as reluctance to cause destruction or coagulation of blood, small capacity, high energy conversion efficiency, etc.